1. Field of the Invention
The present invention relates to a new endless power driving belt having a trapezoidal section, more particularly intended for equipping speed variators with V groove pulleys, for transmitting the movement by contact and pressure in the groove of said pulleys and a method of manufacturing such a belt.
2. Description of the Prior Art
Belts are already known including a reinforcement member formed by one or more metal cables or the like which is equipped with transverse elements made from metal or from another material having good mechanical strength characteristics integrally joined together and with the carrier by means of an elastomer.
The patent FR-A-No. 2 437 531 (VARITRAC) discloses a metal reinforcement member which is formed by steel wires buried in a continuous longitudinal rubber strip, which is disposed in lateral slits formed in the transverse elements, these latter having a trapezoidal form whose small base constitutes the lower part of each transverse element. The connection by adhesion of the surfaces of the rubber strip, of the steel wires and of the transverse elements is obtained by forming them as an integral unit in which the rubber from which the strip is formed extends laterally between the transverse elements at least as far as the opposite side edges of these elements and at least over a part of the parallel side walls which border the recesses, in the gaps between the transverse elements to said side walls of which the rubber adheres.
In the construction disclosed in the VARITRAC patent, consequently, the metal reinforcement cables do not rest directly on the transverse elements, which as a general rule are also made from metal, the metal to metal contact of the reinforcement cables and of the edges of the slits of the transverse elements being avoided by interpositioning the rubber strip in which the reinforcement cables are buried.
Considering the fact that the rubber to metal interface is likely to be of a nature to cause destruction of the elastomer if a high tractive force is applied to the belt, by shearing under the effect of the pressure of the cables on the elastomer in the parts thereof the closest to the bottom of the groove of each of the pulleys, the patent FR-A-No. 2 452 035 (DAVID and TETARD) proposes forming a drive belt of trapezoidal section so that the metal reinforcement cables bear on the bottom of the recess formed in each of the transverse metal elements, these latter having a recess open towards their top part with a bottom substantially parallel to the upper and lower edges of the element and side edges substantially parallel to the oblique lateral sides of the element.
Such a structure of V belt transverse elements was already known from the patent GB-A-No. 655173 (PETER and PETER), although the transverse elements described in this patent are made from leather, synthetic material or vulcanized fibers and are mounted fixed or freely movable on an endless strip formed by a continuous strip, or by the juxtaposition of textile or metal cables in an endless layer or with the ends joined together.
The construction disclosed in the DAVID and TETARD patent has however proved to have considerable drawbacks: in a speed variator, a continuous speed variation over a considerable range of variation means that the belt is subjected to high lateral tensile and compression forces exerted by the flanges of the pulleys with which they cooperate and one at least of which, slideably mounted, is subjected to the action of a hydraulic control jack; the belt is thus subjected to high stresses which may lead to its breakage, which is promoted by the fact that the deformation resulting from the thrust exerted by the jack is aggravated by the arrangement of the reinforcement cable or cables in turns adjacent a single helical winding, which results in giving the transverse elements an orientation in the direction of the helix, which further increases the deformation of the belt, to which is added the metal against metal friction of the reinforcement cable on the bottom of the recess of each transverse element, which causes the premature wear of the cables. Furthermore, with the exception of the PETER and PETER patent, the prior documents are silent as to the means for retaining the cable or cables forming the reinforcement member after tensioning thereof and prior to the positioning of the elastomer. When such retention is obtained by crimping the ends of the cable or cables forming the reinforcement member, breakages of said member are frequently observed after an operating time very appreciably less than that which is expected of such belts in the speed variator mechanisms which they equip.
For such applications, in particular, but generally for a good power transmission which is an indispensible condition of the use of belts, it is important that their lateral sides have as good a surface contact as possible with the internal faces of the flanges of the pulleys on the one hand, and on the other hand, that the transverse elements keep their direction of orthogonality with respect to the meridian plane of the belt, that is to say that during operation there does not occur skewing of the belt with respect to the flanges of the pulleys. In so far as this latter condition is concerned, it should be recalled that the operation of the belt implies the existence of a possibility of relative movement of the transverse elements or plates with respect to the longitudinal reinforcement member, so that the problem raised is not that of giving the transverse elements good perpendicularlity with respect to the meridian plane of the belt during manufacture thereof, which may be provided without great difficulty, but of guaranteeing this positioning is kept during operation.
Another condition imposed on such belts, particularly those immersed in a liquid bath, such as oil at 120.degree. C., is to reduce as much as possible the hydrodynamic resistance phenomena which result, because of stirring of said bath by the wings of the transverse elements or plates, the appearance of noises, on the one hand, and a reduction of the transmission efficiency, on the other.
The present invention provides then a trapezoidal or V power transmission belt which answers better the requirements of practice than the best of the solutions provided in the prior art, particularly in that it withstands the side thrust forces even applied with great force, in that it avoids premature wear of the reinforcement cables, in that it practically eliminates the risk of deformation of the belt, in that it maintains the structural integrity of its reinforcement member even after an extended operating time and in that it provides excellent drive not only in so far as the efficiency is concerned but also the absence of noise or other disturbing factors.
Another aim of the invention is to provide a method of manufacturing such an improved driving V belt.